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<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">另外，对于每个可为空的字段，还有函数可以把该字段设置为</span><span lang="EN-US">null</span><span style="FONT-FAMILY: 宋体">，并检查该字段是否为</span><span lang="EN-US">null</span><span style="FONT-FAMILY: 宋体">。下面的示例列出了</span><span lang="EN-US">SupplierID</span><span style="FONT-FAMILY: 宋体">列的函数：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">[System.Diagnostics.DebuggerStepThrough()]</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">public class ProductRow : DataRow</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">{</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> private ProductDataTable tableProduct;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> internal ProductRow(DataRowBuilder rb) : base(rb)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> this.tableProduct = ((ProductDataTable)(this.Table));</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> public int ProductID</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> get { return ((int)(this[this.tableProduct.ProductIDColumn])); }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> set { this[this.tableProduct.ProductIDColumn] = value; }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> // Other column accessors/mutators removed for clarity</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> public bool IsSupplierIDNull()</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> return this.IsNull(this.tableProduct.SupplierIDColumn);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> public void SetSupplierIDNull()</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> this[this.tableProduct.SupplierIDColumn] = System.Convert.DBNull;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">}</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">下面的代码利用</span><span lang="EN-US">XSD</span><span style="FONT-FAMILY: 宋体">工具中的类的输出从</span><span lang="EN-US">Product</span><span style="FONT-FAMILY: 宋体">表中检索数据，并在控制台上显示这些数据：</span></p>
<p class="a6" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">using System;</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">using System.Data;</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">using System.Data.SqlClient;</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> </span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">public class XSD</span><span lang="EN-US" style="FONT-FAMILY: 'Baskerville BE Regular'">_</span><span lang="EN-US">DataSet</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">{</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> public static void Main()</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> {</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> string source = "server=(local)\\NetSDK;" +</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> "uid=QSUser;pwd=QSPassword;" + </span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> "database=northwind";</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> string select = "SELECT * FROM Products";</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> SqlConnection conn = new SqlConnection(source);</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> SqlDataAdapter da = new SqlDataAdapter(select , conn);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> Products ds = new Products();</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> da.Fill(ds , "Product");</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> foreach(Products.ProductRow row in ds.Product )</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> Console.WriteLine("'{0}' from {1}" , </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> row.ProductID ,</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> row.ProductName);</span></p>
<p class="a6" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> }</span></p>
<p class="a6" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">}</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">重要的代码已突出显示出来了。</span><span lang="EN-US">XSD</span><span style="FONT-FAMILY: 宋体">文件的输出结果包含一个派生于</span><span lang="EN-US">DataSet</span><span style="FONT-FAMILY: 宋体">的类</span><span lang="EN-US">Products</span><span style="FONT-FAMILY: 宋体">，使用数据适配器来创建和填充这个类。</span><span lang="EN-US">foreach</span><span style="FONT-FAMILY: 宋体">语句使用了强类型化的</span><span lang="EN-US">ProductRow</span><span style="FONT-FAMILY: 宋体">和</span><span lang="EN-US">Product</span><span style="FONT-FAMILY: 宋体">属性，返回</span><span lang="EN-US">Product</span><span style="FONT-FAMILY: 宋体">数据表。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">要编译这个示例，执行下面的命令：</span></p>
<p class="a6" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><strong><span lang="EN-US">xsd product.xsd /d</span></strong></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">和</span></p>
<p class="a6" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><strong><span lang="EN-US">csc /recurse:*.cs</span></strong></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">第一个命令从</span><span lang="EN-US">Products.XSD</span><span style="FONT-FAMILY: 宋体">模式中生成</span><span lang="EN-US">Products.cs</span><span style="FONT-FAMILY: 宋体">文件，然后，</span><span lang="EN-US">csc</span><span style="FONT-FAMILY: 宋体">命令使用</span><span lang="EN-US">/recurse:*.cs</span><span style="FONT-FAMILY: 宋体">参数查找扩展名为</span><span lang="EN-US">.cs</span><span style="FONT-FAMILY: 宋体">的文件，并把它们添加到所生成的程序集中。</span></p></div>
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